Polymeric Materials for Corrosion Control - American Chemical Society

29 Structure-Property Relationships in Tin-Based Antifouling Paints 1

1

2

2

D. Ibbitson , A. F. Johnson , N. J . Morley , and A. K. Penman 1

School of Polymer Science, University of Bradford, Bradford, BD7 1DP, England

2

Downloaded by UNIV LAVAL on July 13, 2016 | http://pubs.acs.org Publication Date: October 14, 1986 | doi: 10.1021/bk-1986-0322.ch029

International Paint P L C , Stoneygate Lane, Felling, NE10 OJY, England

Compositionally homogeneous copolymers from tributyltin methacrylate and methylmethacrylate and compositionally homogeneous and heterogeneous terpolymers of tributyltin methacrylate, methyl methacrylate and 2-ethyl hexyl acrylate have been synthesised and the thermal and mechanical properties of the polymers, and paints made from these polymers, measured in relation to polymer composition and composition distribution. The self polishing and anti-fouling characteristics of the materials have also been examined. It has been shown that there are marginal advantages to be obtained in the use of compositionally controlled multicomponent polymers for anti-fouling paints.

The p r o t e c t i o n a g a i n s t c o r r o s i o n o f s h i p s a n d o t h e r m a r i n e e q u i p m e n t makes demands o n t h e p r o t e c t i v e c o a t i n g s o v e r a n d a b o v e t h o s e w h i c h m i g h t be e x p e c t e d f o r l a n d b a s e d m e t a l s t r u c t u r e s . Whatever t h e environment, m e c h a n i c a l damage t o t h e p r o t e c t i v e c o a t i n g through impact is probably the major cause of their failure and c o n s e q u e n t i a l c o r r o s i o n a t t h e s i t e o f damage. With s h i p s there a r e unique problems w i t h those p a r t s o f t h e s t r u c t u r e which r e s i d e below the w a t e r - l i n e i n t h a t t h e metal substrates i n t h i s s i t u a t i o n not o n l y h a v e t o w i t h s t a n d i m p a c t damage b u t m u s t a l s o r e s i s t f o u l i n g b y marine organisms. The i d e a l c o a t i n g s h o u l d p r o v i d e b o t h c o r r o s i o n and a n t i - f o u l i n g r e s i s t a n c e . T h e m o s t common p r a c t i c a l s o l u t i o n t o the problem is to apply two c o a t i n g s , the f i r s t which is specifically aimed a t c o r r o s i o n p r o t e c t i o n and t h e second which provides protection against a n t i - f o u l i n g . Our concern here i s w i t h anti-fouling coatings only. Fouling of hulls leads to a s i g n i f i c a n t increase i n the surface roughness which i n t u r n i n t r o d u c e s an economic p e n a l t y f o r s h i p owners. The i m p o r t a n c e o f s u r f a c e r o u g h n e s s h a s been r e v i e w e d by C h r i s t i e { ! ) , who a l s o d e s c r i b e s t h e d e v e l o p m e n t o f s e l f p o l i s h i n g

0097-6156/ 86/ 0322-0327506.00/ 0 © 1986 American Chemical Society

Dickie and Floyd; Polymeric Materials for Corrosion Control ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

328

POLYMERIC MATERIALS FOR CORROSION CONTROL


copolymer (SPC) anti-foul1ng paints which prevent fouling over e x t e n d e d p e r i o d s and w h i c h a l s o d e c r e a s e t h e s u r f a c e roughness of hulls in service. These p a i n t s have e v o l v e d f r o m t h e work of Montermoso e t al (2) and were d e v e l o p e d i n t o commercial selfp o l i s h i n g p a i n t s y s t e m s by M i l n e and H a i l s ( 3 ) . The b e n e f i t s o f self p o l i s h i n g p a i n t s s y s t e m s a r e now w i d e T y ~ ~ r e c o g n i s e d a n d SPC paints hold a major share of the a n t i - f o u l a n t market. G e n e r a l l y , a n t i f o u l i n g c o a t i n g s c o n t a i n i n g o r g a n o t i n c o m p o u n d s may be divided into two types: polishing and non-polishing. In c o n v e n t i o n a l n o n - p o l i s h i n g p a i n t s t h e t i n compounds a r e p h y s i c a l l y trapped i n t o a polymer matrix and t h e a n t i - f o u l i n g b e h a v i o u r is d e p e n d e n t on t h e l e a c h i n g o f t h e b i o c i d e f r o m t h e m a t r i x . With s e l f - p o l i s h i n g p a i n t s t h e a n t i - f o u l i n g m e c h a n i s m i s more c o m p l e x . The b i o c i d e i s a t t a c h e d t o t h e p o l y m e r s u b s t r a t e a n d h a s t o b e released by a hydrolysis mechanism. The hydrolysis reaction m o d i f i e s t h e s u r f a c e o f p o l y m e r making i t h y d r o p h i l i c and t h e r e f o r e m o r e s u s c e p t i b l e t o r e m o v a l by t h e f r i c t i o n a l f o r c e s d e v e l o p e d a t t h e h u l l - w a t e r i n t e r f a c e when a s h i p moves t h r o u g h w a t e r . Recently, concern has been expressed about possible environmental problems which might r e s u l t from the r e l e a s e of those p a i n t s i n w h i c h t h e t i n compounds a r e n o t c h e m i c a l l y bonded t o t h e base polymer. O b v i o u s l y i t i s d e s i r a b l e t o r e d u c e t h e amount o f b i o c i d a l l y a c t i v e material from a n t i - f o u l i n g paints to the lowest practicable level. An understanding of the structure property-relationships i n the copolymer or multicomponent polymers w h i c h a r e u s e d i n SPC p a i n t s i s e s s e n t i a l i n o r d e r t o make t h e m o s t effective use of the biocide. To fully evaluate the structure-property r e l a t i o n s h i p s , i t i s necessary to decouple a very large number of interacting parameters, for example, molecular features such as chemical composition, chemical composition d i s t r i b u t i o n o r m o l e c u l a r w e i g h t and t h e i r i n f l u e n c e on polymer h y d r o p h i l i c i t y , f i l m forming character or mechanical p r o p e r t i e s . It i s almost i n e v i t a b l e w i t h such a complex s e t of i n t e r a c t i n g f a c t o r s that there will b e no s i n g l e ideal polymer structure for all p u r p o s e s b u t r a t h e r t h a t t h e r e m i g h t be some o p t i m u m s t r u c t u r e w h i c h s a t i s f i e s a number o f t h e m a j o r c r i t e r i a f o r any g i v e n end u s e . An e a r l y s t u d y o f t h e i n f l u e n c e o f c o m p o s i t i o n h e t e r o g e n e i t y on t h e p h y s i c a l p r o p e r t i e s o f c o p o l y m e r s was u n d e r t a k e n b y N i e l s o n ( 4 ) , b u t t o t h e k n o w l e d g e o f t h e a u t h o r s , t h e r e h a v e b e e n no s i m i l a r i n v e s t i g a t i o n s i n v o l v i n g tin-based polymers. In t h i s work a r a n g e o f d i f f e r e n t a c r y l i c c o - and t e r p o l y m e r s has been p r e p a r e d and t h e e f f e c t s o f c o m p o s i t i o n and c o m p o s i t i o n d i s t r i b u t i o n on t h e p h y s i c a l and p e r f o r m a n c e - r e l a t e d p r o p e r t i e s o f t h e p o l y m e r s i n t h e i r native s t a t e and i n p a i n t s have been e x a m i n e d . As a n e c e s s a r y p r e l i m i n a r y t o t h e s t u d y o f how c o m p o s i t i o n a l heterogeneity affects the properties of the polymers, c o m p o s i t i o n a l l y h e t e r o g e n e o u s and homogeneous c o - and terpolymers had t o be s y n t h e s i s e d . I t i s common i n c o p o l y m e r i s a t i o n s f o r t h e s o t h a t r e l a t i v e r e a c t i v i t y o f t h e c o - m o n o m e r s t o b e d i f f e r e n t (5± during polymerisations carried out to high conversion in a f r e e - r u n n i n g batch r e a c t o r , the i n i t i a l l y formed polymer i s r i c h e r i n t h e more r e a c t i v e monomer, w h e r e a s , a t t h e end o f t h e r e a c t i o n the polymer produced contains a g r e a t e r proportion of the less reactive monomer. In such circumstances, compositional


29.

IBBITSON ET AL.

329

Tin-Based Antifouling Paints

heterogeneity i s inevitable from such a p r o c e s s .

i n the

polymer which

is

finally

isolated


Compositionally uniform copolymers of tributyltin methacrylate (TBTM) a n d m e t h y l m e t h a c r y l a t e (MMA) a r e p r o d u c e d i n a f r e e r u n n i n g b a t c h p r o c e s s by v i r t u e o f t h e monomer r e a c t i v i t y r a t i o s f o r this c o m b i n a t i o n o f monomers ( r (TBTM) = 0 . 9 6 , r (MMA) = 1 . 0 a t 8 0 ° C ) . C o m p o s i t i o n a l l y h o m o g e n e o u s t e r p o l y m e r s w e r e s y n t h e s i s e d by k e e p i n g constant the instantaneous ratio of the three monomers in the reactor through the addition of t h e more reactive monomer (or monomers) a t an a p p r o p r i a t e r a t e . T h i s p r o c e d u r e h a s b e e n u s e d by Guyot et al (§X i n the preparation of butadiene-acrylonitrile emulsion copolymers and by Johnson et al {7)_ i n the solution c o p o l y m e r i s a t i o n o f styrene w i t h methyl a c r y l a t e . EXPERIMENTAL MODELLING AND SIMULATION

The m o d e l l i n g t e c h n i q u e s w h i c h a r e commonly u s e d f o r p o l y m e r i s a t i o n r e a c t i o n s have been r e v i e w e d ( 8 ) . D e t e r m i n i s t i c a n a l y t i c a l models b a s e d on t h e d e t a i l e d c h e m i s t r y o f c o - and t e r p o l y m e r i s a t i o n s have been used t o a s s i s t w i t h t h e d e s i g n o f r e a c t o r c o n d i t i o n s f o r t h e synthesis of polymers with s p e c i f i c c o m p o s i t i o n and structure. T y p i c a l d a t a u s e d w i t h t h e s e m o d e l s a r e shown i n T a b l e 1 . Simpler mass b a l a n c e m o d e l s h a v e b e e n u s e d f o r t h e d e s i g n o f r e a c t o r c o n t r o l strategies for the production of compositionally homogeneous polymers. For control purposes, use has been made of the o b s e r v a t i o n t h a t f o r many t e r p o l y m e r i s a t i o n s ( a n d c o p o l y m e r i s a t i o n s , a l t h o u g h c o n t r o l was u n n e c e s s a r y f o r t h e monomer c o m b i n a t i o n u s e d i n t h i s w o r k ) i n d i v i d u a l monomers a r e c o n s u m e d b y an a p p a r e n t first order process. When t h i s s i t u a t i o n p e r t a i n s ( a n d i f t h e r e a c t o r i s a s s u m e d t o be i s o t h e r m a l a n d t h e i n i t i a t o r h a s a l o n g half-life) t h e n i t may be shown ( 9 ) t h a t t h e f o l l o w i n g e q u a t i o n s a r e t r u e f o r t e r p o l y m e r i s a t i o n s c a r r i e d out i n a semi-batch r e a c t o r . dA/dt

= -kl*A + F(l)

*

dB/dt

= -k2*B + [ F ( l )

+ F(2)]

dC/dt

= -k3*C + F(2)

+ C(F)

A(F)

+ [F(l)

+ F(2)]

* A/V

* B/V

+ TF(1)

(1) (2)

+ F(2)^

* C/V

(3)

w h e r e t h e monomer f e e d s a r e F ( l ) = T A / A ( F ) 1 * ( k l - k 2 ) a n d F ( 2 ) = r c / C ( F ) ] * ( k 3 - k 2 ) a n d k l , k2 a n d k 3 a r e a p p a r e n t f i r s t order rate constants for i n d i v i d u a l monomers b u t a t a s p e c i f i c monomer composition. In these equations the three monomer c o n c e n t r a t i o n s ( m o l e s ) a r e d e s i g n a t e d by A Β and C and i t i s assumed t h a t Β r e a c t s more s l o w l y t h a n A a n d C. The c o n c e n t r a t i o n o f t h e m o r e r e a c t i v e monomers i n t h e f e e d s a r e A ( F ) a n d C ( F ) ( m o l e s / 1 ) a n d F(l) and F ( 2 ) a r e t h e f e e d r a t e s ( 1 / m i n ) . These e q u a t i o n s d e f i n e t h e f e e d p r o f i l e f o r t h e p r o d u c t i o n o f c o r n p o s i t i o n a l l y homogeneous products. Precise k i n e t i c constants are necessary in order to execute effective experimental control of the polymersiation r e a c t o r s a n d t h e m e t h o d s u s e d t o o b t a i n t h e s e d a t a a n d some t y p i c a l c o n s t a n t s f o r one t e r n a r y s y s t e m a r e r e p o r t e d overleaf.


330



Table 1.

K i n e t i c parameters used i n s i m u l a t i o n s t u d i e s of c o p o l y m e r ! s a t i o n o f MMA w i t h TBTM.

kd

1.50.10

exp(-30800/RT)

s

kll

3.20.10

exp(-7000/RT)

l/s/mol

kl2

1.75.10

exp(-9480/RT)

l/s/mol

k21

4.20.10

exp(-7520/RT)

l/s/mol

k22

6.60.10

exp(-6300/RT)

l/s/mol

ktll

=

1.23.10

exp(-3000/RT)

l/s/mol

kt22

=

1.77.10

exp(-2840/RT)

l/s/mol

ktl2

=

(ktll*kt22)

the

Monomer 1 = MMA a n d monomer 2 = TBTM kll

= homopolymerisation

constant

for

monomer 1

k22 = h o m o p o l y m e r i s a t i o n

constant

for

monomer 2

propagation

constants

k l 2 and k21 a r e

the

cross

k t l 2 an a v e r a g e

termination

constant

A f u l l d e s c r i p t i o n o f t h e m o d e l l i n g and c o n t r o l o f m u l t i c o m p o n e n t p o l y m e r i s a t i o n s i s beyond t h e scope o f t h i s p r e s e n t a t i o n s i n c e t h e r e a r e many e x c e p t i o n s t o t h e a b o v e s i m p l i s t i c m o d e l h e n c e d e t a i l s w i l l be d e s c r i b e d e l s e w h e r e (9). POLYMER

SYNTHESIS

All polymerisations were c a r r i e d out in nitrogen purged xylene s o l u t i o n s i n a t h e r m o s t a t i c a l l y c o n t r o l l e d one l i t r e g l a s s r e a c t o r . S e m i - b a t c h p r o c e s s e s w e r e c a r r i e d o u t i n a s i m i l a r r e a c t o r w h i c h was p r o v i d e d w i t h c a l i b r a t e d p e r i s t a l t i c pumps ( c o m p u t e r c o n t r o l l e d when n e c e s s a r y ) f o r d e l i v e r i n g t h e monomer f e e d s . T y p i c a l l y , experiments w e r e c a r r i e d o u t a t 8 0 ° C w i t h monomer c o n c e n t r a t i o n s w h i c h gave s o l i d s c o n t e n t s i n t h e r a n g e 10 - 60% a t 100% c o n v e r s i o n . The c o n t r o l s t r a t e g i e s f o r d e t e r m i n i n g t h e f e e d p o l i c i e s w e r e decided on the basis of a numerical solution of the terpolymerisations described by equations 1 - 3 using a microcomputer and a g e n e r a l purpose simulation package, BEEBS0C (10). Where n e c e s s a r y , t h e s e d a t a w e r e a c q u i r e d i n t h e c o u r s e o f t h i s study, otherwise l i t e r a t u r e v a l u e s were u s e d . The apparent f i r s t o r d e r r a t e c o n s t a n t s i n t e r p o l y m e r i s a t i o n s h a v e b e e n shown t o be c o m p o s i t i o n d e p e n d e n t . The v a r i a t i o n in rate constants with


29.

IBBITSON ET AL.


composition

at

80°C

k(MMA)

=

k(TBTM) k(2EHA)

331

Tin-Based Antifouling Paints can

-0.025

be

described

by

the

following

equations:

* X

+

0.0346

(4)

=

0.036 * X

+

0.0065

(5)

=

0.056 * X

+

0.0062

(6)

where k( ) i s t h e a p p a r e n t r a t e c o n s t a n t and X t h e i n i t i a l weight f r a c t i o n o f t h e r e s p e c t i v e monomer i n t h e r e a c t o r f e e d . The f o l l o w i n g m a t e r i a l s were used as s u p p l i e d : tributyltin methacrylate (International Paint pic), 2-ethylhexyl acrylate (Aldrich Chemical Co. Ltd.), methyl methacrylate (ICI pic) s u l p h u r - f r e e x y l e n e a n d c h l o r o f o r m (May arid B a k e r L t d . ) . POLYMER

CHARACTERISATION

A number o f methods w e r e e x p l o r e d f o r m o n i t o r i n g t h e p r o g r e s s of polymerisations. In e a c h c a s e s a m p l e s were removed f r o m t h e r e a c t o r at appropriate time i n t e r v a l s and a n a l y s e d o f f - l i n e . Gas-liquid chromatography proved t o be u n r e l i a b l e f o r analysis of residual monomer concentrations because of monomer d e c o m p o s i t i o n on the c o l u m n s and t h e r e l a t i v e l y low v o l a t i l i t y of the tin-containing monomer. G r a v i m e t r i c a n a l y s i s o f t h e p o l y m e r p r o d u c e d w i t h t i m e by p r e c i p i t a t i o n was a l s o shown t o b e i n a c c u r a t e , p a r t i c u l a r l y a t l o w conversion, because of incomplete i s o l a t i o n of lower molecular w e i g h t m a t e r i a l a n d t h e r e t e n t i o n o f r e s i d u a l s o l v e n t a n d monomer by t h e p r e c i p i t a t e . The p o l y m e r i s a t i o n s w e r e s u c c e s s f u l l y f o l l o w e d using gel permeation chromatography (GPC) to monitor residual monomers. The c h r o m a t o g r a p h ( W a t e r s A s s o c i a t e s ) was f i t t e d w i t h PL G e l columns (Polymer L a b o r a t o r i e s L t d . ) and two i n f r a r e d d e t e c t o r s in series. C h l o r o f o r m was u s e d a s t h e e l u a n t . I n f r a r e d d e t e c t o r s were u s e d b e c a u s e t h e t i n c o n t a i n i n g a c r y l i c monwner h a s a c h a r a c t e r i s t i c carbonyl s t r e t c h i n g frequency a t 1 6 2 0 cm which i s well removed f r o m t h a t o f o t h e r a c r y l i c monomers w h i c h h a v e , c a r b o n y l absorptions a t t h e more c h a r a c t e r i s t i c w a v e n u m b e r 1 7 2 0 cm" . Both peaks obeyed the Beer Lambert law. A t y p i c a l chromatogram showing the s e p a r a t i o n o f r e s i d u a l monomers a n d p o l y m e r i s shown i n F i g u r e 1 . POLYMER

TESTING

P o l y m e r f i l m s o f a p p r o x i m a t e l y 1000 m i c r o n s wet f i l m t h i c k n e s s were l a i d down w i t h a b a r a p p l i c a t o r o n P T F E c o a t e d g l a s s p a n e l s a n d t h e s o l v e n t allowed to evaporate a t ambient temperature f o r a standard p e r i o d of seven days. A t y p i c a l p l o t of solvent weight loss with t i m e i s shown i n F i g u r e 2. The t h i c k n e s s o f t h e w e t f i l m was d i c t a t e d by t h e n e e d t o h a v e a d e q u a t e m e c h a n i c a l s t r e n g t h i n t h e d r y f i l m s i n o r d e r t h a t t h e y m i g h t be s u i t a b l e f o r s u b s e q u e n t m e c h a n i c a l test procedures. Dry film thicknesses were a p p r o x i m a t e l y 300 m i c r o n s a s m e a s u r e d by m i c r o m e t e r . The d r i e d p o l y m e r f i l m s w e r e examined by d y n a m i c m e c h a n i c a l t h e r m a l analysis (DMTA) (Polymer Laboratories Ltd.). T y p i c a l DMTA d a t a f o r a p o l y m e r a n d p a i n t a r e


332


shown i n F i g u r e 3 . T e n s o m e t r y ( I n s t r o n M o d e l 1 0 2 6 ) was u s e d t o o b t a i n m e c h a n i c a l p e r f o r m a n c e d a t a on b o t h p o l y m e r a n d p a i n t f i l m s .


PAINT PREPARATION

AND T E S T I N G

P a i n t s were prepared from polymers of d i f f e r e n t c o m p o s i t i o n and composition d i s t r i b u t i o n u s i n g a standard copper t h i o c y a n a t e based f o r m u l a t i o n s i m i l a r t o t h a t w h i c h h a s b e e n d e s c r i b e d by H a i l s a n d Symonds ( 1 1 ) . A r o t a t i n g d i s c t e c h n i q u e ( 3 ) was u s e d t o m e a s u r e t h e p o l i s h i n g r a t e (which i s a measure o f h y d r o l y s i s r a t e ) o f polymer and p a i n t f i l m s . S t a n d a r d c o a t e d p a n e l s were a t t a c h e d t o a d i s c ( F i g u r e 4) i n a r a d i a l d i s p l a y and t h i s d i s c t h e n r o t a t e d a t a constant s p e e d ( 1 4 0 0 rpm) in a thermostatically controlled tank ( 2 5 ° C ) of r e p l e n i s h e d sea w a t e r . They h y d r o l y t i c s t a b i l i t y o f t h e films was a s s e s s e d b y t h e r a t e o f c h a n g e o f f i l m t h i c k n e s s a s measured by a s u r f a c e p r o f i l i n g t e c h n i q u e ( F e r r a n t i Surfcom). A n t i - f o u l i n g t e s t s w e r e c a r r i e d o u t on b r u s h c o a t e d plastic laminate panels which had been given a primary coating of anti-corrosion paint. Performance was measured by visual o b s e r v a t i o n s o f t h e p a n e l s a f t e r p r o l o n g e d i m m e r s i o n (4 - 12 m o n t h s ) i n a known h i g h - f o u l i n g e s t u a r i n e e n v i r o n m e n t . RESULTS AND

DISCUSSION

The r e l a t i v e r e a c t i v i t y o f TBTM a n o MMA i s s u c h t h a t c o m p o s i t i o n a l l y homogeneous copolymers are produced to complete conversion of monomers i n a f r e e - r u n n i n g b a t c h r e a c t o r . The r e a c t i v i t y o f 2EHA i s s i g n i f i c a n t l y l e s s t h a n t h a t o f e i t h e r o f t h e o t h e r two monomers i n ternary polymerizations and control action is required during polymerization in order to produce homogeneous products. The i n f l u e n c e o f c o n t r o l l e d monomer f e e d on t h e i n s t a n t a n e o u s r a t i o o f c o r e a c t a n t s c a n be s e e n i n F i g u r e 5 . The r a t i o o f MMA t o 2EHA r e m a i n s c o n s t a n t t h r o u g h o u t t h e r e a c t i o n w i t h c o n t r o l l e d MMA f e e d t o the reactor and t h e ratio of TBTM t o 2EHA i s constant up to approximately 97% c o n v e r s i o n o f monomers w i t h a c o n t r o l l e d TBTM feed. The s m a l l a m o u n t o f u n c o n t r o l l e d m a t e r i a l w h i c h i s i n t r o d u c e d into the product beyond 97% c o n v e r s i o n has been considered insignificant. The e r r o r i n m a k i n g a b s o l u t e m e a s u r e s o f r e s i d u a l monomer c o n c e n t r a t i o n s by GPC i n c r e a s e s a s t h e c o n c e n t r a t i o n s o f t h e monomers d e c r e a s e s a n d t h e r a t i o o f two i n a c c u r a t e s m a l l n u m b e r s c a n be m i s l e a d i n g a n d p r o b a b l y i s r e s p o n s i b l e f o r t h e l a r g e d e v i a t i o n shown i n t h e TBTM/2EHA r a t i o a t c o n v e r s i o n s >97%. Glass transition data for copolymers and terpolymers of c o n t r o l l e d a n d u n c o n t r o l l e d c o m p o s i t i o n a r e shown i n F i g u r e s 6 a n d 7. The T g ' s c a l c u l a t e d u s i n g t h e e q u a t i o n s 7 a n d 8 o f Fox ( 1 2 ) a n d Woods ( 1 3 ) h a v e b e e n u s e d w i t h t h e f o l l o w i n g h o m p o l y m e r T g ' s ; methyl methacrylate, 108°C; tributyltin methacrylate, 0°C; 2-ethylhexyl a c r y l a t e , - 5 0 ° C ( 1 4 - 1 6 ) a r e a l s o shown. Tg

= w(l).

Tg

= ΓΑ(1).

Tg(l)

+ w(2).

Tg(2)

w(l)/Tg(l)?+rA(2).

+ w(3).

Tg(3)

w(2)/Tg(2)]

+ ΓΑ(3).

(7) w(3)/Tg(3)]

(8)

In e q u a t i o n s 7 a n d 8 w ( i ) , Tg(i) and A ( i ) a r e t h e w e i g h t fraction and g l a s s t r a n s i t i o n s o f monomer w h e r e 1 = 1 , 2 o r 3 a n d A ( i ) i s a n adjustable parameters.


IBBITSON ET AL.

333


Elution Volume


FIGURE

1.

T y p i c a l GPC c h r o m a t o g r a m s o f r e s i d u a l monomers w i t h d e t e c t o r 1 s e t a t 1720 c m ( - l ) and d e t e c t o r 2 a t 1620 cm(-l). C o l u m n s ; 1 0 , 1 0 0 , 1,000 and 1 0 , 0 0 0 n m . , e a c h 30cm l o n g a n d p a c k e d w i t h 1 0 μ g e l particles.

2.LY

Solvent Loss

2.2

2.0| cr>

Dry Weight Ξ

1JB

Ε il 1.6

U 5

FIGURE 2 .

Typical ambient

1 0 *~

Days

s o l v e n t l o s s (by w e i g h t ) f r o m a t h i n f i l m a t temperature. Weight o f dry material.

0.6 Polymer T

σ 0Â

g

56°C

/" V

-.^

P a , n t

T

/

g

6A°C

0.2

0.0

FIGURE 3 .

20 Typical

AO 60 Temperature (°C ) DMTA d a t a f o r

80

t e r p o l y m e r and p a i n t .


100

334



(b)

FIGURE

4.

Schematic diagram of r o t a t i n g d i s c p o l i s h i n g equipment. R o t o r speed 1400 r p m , t e m p e r a t u r e 2 5 ° C . (a) p l a n v i e w o f d i s c and samples (b) s i d e v i e w o f d i s c mounted i n w a t e r t a n k .

FIGURE

5.

Monomer r a t i o i n c o n t r o l l e d ( C ) a n d u n c o n t r o l l e d (U) t y p i c a l terpolymerisation taken to high conversion. C o n t r o l was a c h i e v e d by f e e d i n g b o t h TBTM a n d MMA t o a semi-batch reactor at 80°C. Monomer ratios m e a s u r e d by G P C .



29.

IBBITSON ET AL.


335

T h e r e a p p e a r t o b e no r e p o r t e d v a l u e s f o r t h e Tg o f p o l y ( T B T M ) and i t p r o v e d d i f f i c u l t t o measure any m e a n i n g f u l t r a n s i t i o n by d i f f e r e n t i a l scanning calorimetry. The v a l u e o f 0 ° C was s e l e c t e d a s i t g a v e a r e a s o n a b l e f i t t o e x p e r i m e n t a l d a t a when u s i n g e q u a t i o n s 7 and 8 . F o r b o t h t h e b i n a r y and t e r n a r y s y s t e m s t h e t r e n d s i n t h e Tg's a r e a s m i g h t be e x p e c t e d i n a q u a l i t a t i v e s e n s e . Neither equation 7 n o r 8 g i v e good f i t s t o t h e e x p e r i m e n t a l d a t a o v e r t h e c o m p l e t e c o m p o s i t i o n range f o r e i t h e r the b i n a r y o r t e r n a r y copolymer cases but the general trend i n Tg's w i t h c o m p o s i t i o n i s a s m i g h t be predicted. These e q u a t i o n s are s e n s i t i v e to the v a l u e s o f the homopolymer Tg's u s e d . T h e r e i s no o b v i o u s r e a s o n why t h e r e s h o u l d be s u c h a s h a r p c h a n g e i n t h e o b s e r v e d T g ' s a t about 0 . 5 mole percent of methyl methacrylate and f o r the binary polymer our o b s e r v a t i o n s c a n be a t t r i b u t e d t o t h e s m a l l amounts o f residual s o l v e n t w h i c h r e m a i n s i n t h e p o l y m e r s u s i n g t h e m e t h o d s we h a v e adopted to produce the polymer (and p a i n t ) f i l m s used f o r the analyses. I n t h e c o m m e r c i a l c o n t e x t , p a i n t f i l m s a r e a s s u m e d t o be dry in a relatively short time a f t e r a p p l i c a t i o n (24 h o u r s or less). S h i p s may e n t e r s e r v i c e w e l l w i t h i n t h e t i m e s c a l e o f t h e seven day d r y i n g p e r i o d used f o r our l a b o r a t o r y prepared f i l m s . Although the solvent removal rate i s very rapid i n i t i a l l y , the d i f f u s i o n r a t e o f s o l v e n t f r o m t h e f i l m soon becomes v e r y s l o w ( s e e Figure 2). A f t e r seven days the f i l m s might r e t a i n between 2-5% s o l v e n t by w e i g h t d e p e n d i n g on t h e c o m p o s i t i o n o f t h e p o l y m e r f r o m w h i c h t h e s o l v e n t has had t o e s c a p e . In t h i s work t h e d a t a have been o b t a i n e d w i t h m a t e r i a l s c o n t a i n i n g 4 . 0 + 0 . 5 % r e s i d u a l s o l v e n t . P r e c i s e s t u d i e s of s o l v e n t evaporation under c o n t r o l l e d c o n d i t i o n s have n o t been c a r r i e d o u t b u t i t i s e v i d e n t t h a t t h e l o w e r t h a n p r e d i c t e d Tg V a l u e s f o r h i g h m e t h y l m e t h a c r y l a t e c o n t e n t c o p o l y m e r s ( F i g u r e 6) r e s u l t s from the p l a s t i c i z i n g e f f e c t o f r e s i d u a l s o l v e n t . I t i s a p p r o p r i a t e t h a t m e a s u r e m e n t s a r e made on p o l y m e r a n d p a i n t f i l m s c o n t a i n i n g r e s i d u a l s o l v e n t a s t h e s e m e a s u r e m e n t s a r e more realistic in relation to t h e end use o f the m a t e r i a l s . For s c i e n t i f i c p u r p o s e s m e a s u r e m e n t s on t h e f u l l y d r i e d f i l m s a r e t h e o n l y ones o f r e l e v a n c e . Some t y p i c a l Tg d a t a f o r f u l l y d r i e d f i l m s a r e shown i n T a b l e 2 . On a v e r a g e t h e o b s e r v e d T g ' s a r e 1 0 ° C h i g h e r t h a n f o r f i l m s c o n t a i n i n g s m a l l amounts o f r e s i d u a l s o l v e n t . What i s n o t known i s t h e c o n t r i b u t i o n t o t h e p r o p e r t i e s o f s l o w s o l v e n t removal from p a i n t f i l m s i n s e r v i c e . In t h e c a s e o f non-self p o l i s h i n g p a i n t s t h e c o n s e q u e n c e s must be a t r e n d t o c o a t i n g s w h i c h a r e more b r i t t l e i n c h a r a c t e r . In t h e c a s e o f s e l f - p o l i s h i n g p a i n t s t h e s i t u a t i o n i s more c o m p l e x i n t h a t t h e s o l u b i l i z i n g e f f e c t o f t h e sea water a t the c o a t i n g - w a t e r i n t e r f a c e i s l i k e l y t o c o u n t e r a c t the e m b r i t t l e m e n t w h i c h m i g h t o t h e r w i s e be o b s e r v e d . What i s a p p a r e n t i s t h a t T g ' s a r e i n s e n s i t i v e t o c o m p o s i t i o n a l heterogeneity of the polymers. T h e r e i s some e v i d e n c e t h a t t h e T g ' s o f c o m p o s i t i o n a l l y homogeneous p o l y m e r s a r e h i g h e r t h a n f o r the heterogeneous m a t e r i a l s but the difference is small. For the comonomer s y s t e m s r e p o r t e d t h i s o b s e r v a t i o n i s n o t t o o s u r p r i s i n g s i n c e t h e r e a c t i v i t y r a t i o s o f TBTM a n d MMA a r e v e r y s i m i l a r . It i s t h e r e a c t i v i t y o f t h e 2EHA w h i c h i s s i g n i f i c a n t l y d i f f e r e n t b u t t h i s monomer i s o n l y i n c o r p o r a t e d t o a r e l a t i v e l y s m a l l e x t e n t ,

Polymeric Materials for Corrosion Control - American Chemical Society

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