Photoinitiated Polymerization - American Chemical Society

Chapter 34

Photocurable, Hydrophobic Oligomers Based on Liquid Polybutadienes

Downloaded by UNIV LAVAL on October 16, 2015 | http://pubs.acs.org Publication Date: March 3, 2003 | doi: 10.1021/bk-2003-0847.ch034

Bo Yang and Bill Schaeffer Sartomer Company, 502 Thomas Jones Way, Exton, PA 19341

Abstract A series of photocurable, hydrophobic oligomers have been synthesized based on liquid polybutadiene prepolymers. The unique polybutadiene backbone chemistry provides films cured from these oligomers with inherent hydrolytic stability, resistance to aqueous acids and bases, low temperature flexibility, low moisture permeability, and dielectric properties. The base prepolymers are functionalized with either (meth)acrylate or epoxy groups making these new oligomers undergo facile photo-induced polymerization by either free radical or cationic mechanism. Basic photocuring behaviors of these oligomers and physical properties of cured films are investigated and reported.

400

© 2003 American Chemical Society

In Photoinitiated Polymerization; Belfield, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2003.

401


Introduction In recent years, photocuring technology has experienced rapid growth in coatings, inks, adhesives, and photolithography. While formulators now make their oligomer choice among commercially available acrylated epoxies, urethanes, polyesters, or polyethers, however, it was well recognized that the range of chemical and mechanical properties obtainable with these conventional materials is limited. For example, because these oligomers are generally hydrophilic in nature, it is difficult to obtain films having high degree of flexibility (especially at low temperature), hydrolytic stability, and dielectric properties. At the same time, functionalized elastomeric polybutadiene resins have been available for a number of years but are usually limited in their functionality to hydroxyl, vinyl, or carboxyl groups. One feasible approach is to incorporate (meth) acrylic ester or epoxy functionality into the elastomeric liquid polybutadiene which then can be photo crosslinked to produce networks which combines the properties of rubbers and (meth)acrylic/epoxy resins. Further, these oligomers are liquid at room temperature and thus can be easily handled by conventional application processes. Similar considerations have led Decker and his coworkers to modify diene polymers by attaching acrylic ester groups and Kennedy et. al. to prepare epoxy techellic poly(isobutylenes). Both of these groups studied the UV induced crosslinking of the functionalized elastomers. In this paper, we describe the basic chemistry of these liquid polybutadiene based elastomeric oligomers. Reactivity of these oligomers under photocuring condition was examined. Difference in photocuring responses between (meth)acrylate and 1, 2 vinyl/1, 4 double bonds was studied. Glass transition temperature, tensile properties, surface hardness, and resistance to acids and bases were measured and discussed. 1

2

Experimental

Materials All liquid polybutadiene oligomers were from Sartomer Company: (meth)acrylated liquid polybutadiene (Ricacryl® 3801); epoxidized liquid polybutadiene (Poly BD® 600E and 605E); liquid polybutadiene dimethacrylate (CN301 and CN303); liquid polybutadiene urethane diacrylate (CN302). Both Ricacryl® and Poly BD® are trademarks of Sartomer Company. Specialty


402 photoinitiator Esacure KIP-100F and cycloaliphatic epoxy SarCat®K126 were also from Sartomer Company. ITX was provided by First Chemical Corporation. Irgacure 651 was supplied by Ciba Specialty Chemicals.

Wet film preparation


For standard fdm testing, a 5 mil wet fdms was cast on mill finished aluminum Q-Panels by using zero drawdown rods with double tapes. Great care was taken to obtainfilmswith uniform thickness. This is very important because film thickness is a critical factor in determining a coating's performance.

Measurement of double bonds conversion Conversion of double bonds from both the (meth)acrylic esters and polybutadiene unsaturation were measured by Fourier Transform Infrared Spectroscopy (FTIR) technique. A MIDAC FTIR spectrometer Model 1012801 was used. An UVEXS Model CCU-A conveyorized unit equipped with a single medium mercury vapor lamp was used to UV cure the samples. The UV dosage was measured using UVPS CON-TROL-CURE Model M007-008 compact radiometer. A detailed description of the technique and experimental results can be foundfromEstrin's original work . 3

UV curing system (for studies other than FTIR) An Asheed UV curing system was used. For physical properties testing, the films were passed four times under two 300W/in Hg lamps. Prior to testing, all the coated panels were stored in the dark after curing for three days. This was done to ensure a uniform environmental history of the samples.

Test for acid and base resistance The test procedure followed ASTM method D 1308-79. 50% sulfuric acid (H S0 ) was used. For tensile measurement,filmstripswere fully immersed in the testing reagents in an amber bottle. The strips were exposed using the same intervals as those for the covered spot test. The strips were washed and dried before testing. 2

4


403 Mechanical Properties Test Tensile strength, elongation, and tensile modulus were determined with a Thwing-Albert tensile tester with a strain rate of 0.5 in/min. For each sample, at least 5 specimens were tested and an average value was reported.


Results and Discussion

1. Basic Chemistry

a. (Meth)acrylated Liquid Polybutadiene Oligomers Ricacryf3801, CN301, CN302, and CN303 are (meth)acrylated liquid polybutadienes. As depicted in Scheme 1, the (meth)acrylate groups are located either terminally or along its linear backbone. For Ricacryl®3801, the oligomeric backbone was further functionalized with amines to render the oligomer adhesion promoting characteristic and aqueous dispersible. General physical properties of these liquid oligomers are described in Table 1.

Scheme 1: Chemical structures of (meth)acrylated liquid polybutadienes

Β

A Ο R = Η for CN302 (acrylate) R= C H for CN301 and CN303 (methacrylates) 3

R

R

R = acrylate, methaciylate or amine group R i c a C f y 1 f


3801

404 Table 1: General physical properties of the (meth)acrylated liquid polybutadiene oligomers Ricacryl 3801 3200 2 6 26 10 25,000 @45°C

Oligomers

unctio ality

a

e

MW Acrylate Methacrylate 1,2 Vinyl Trans 1,4-


Viscosity

CN301

CN302

CN303

3000

3000 2

3000 2

-

-

970 @60°C

17,000 @60°C

4,125 ©60°°

2

-

-

Scheme 2. Epoxidation of Polybutadiene

ο

b. Epoxidized Liquid Polybutadiene Oligomers As shown in Scheme 2, Poly BD® E600 and E605 were obtained by epoxidation of liquid polybutadienes, mainly through 1,4 double bounds. An earlier investigation by Crivello et. al. on a similar epoxidation experiment shown that 1,4 double bonds are much more reactive than 1,2 vinyl double bonds towards epoxidation, mainly due to the higher electronic density associated with the 1,4 double bond. Basic properties of these two oligomers are described in Table 2. 4


405 2. Photo Reactivity and Properties of Cured Films of (Meth)acrylated L i q u i d Polybutadiene Oligomers The photo reactivity of the four (meth)acrylated liquid polybutadiene oligomers werefirstcompared (see Table 3). The order of reactivity is ranked as following: Ricacryr3801 > CN301 - CN303 > CN302.


Table 2 Basic properties of Poly B D E600 and E605

Epoxy Value, meq/g Epoxy Equivalent Weight Oxirane Oxygen % Viscosity mPas @30°C maximum Water, W t , % , maximum Specific Gravity Hydroxyl value (meq/g) Approximate microstructure (mol.)

E605 3-4 260-330 4.8-6.2 22,000 0.10 1.01 1.74

E600 2-2.5 500-400 3.4 7000 0.10 1.01 1.70

Epoxy cis

7 to 10

Epoxy trans

8 to 12

V i n y l double bonds 1,4 - double bonds Opened Epoxy

22 53 to 60 3 to 4

With eight pendant (meth)acrylate groups, Ricacry1*3801 posses the highest reactivity under photo-induced polymerization. The high functionality also contributes to high tensile and modulus but an accordingly lower elongation. It is interesting to note that a glass transition temperature of -18.2°C was recorded with such a highly crosslinked polymeric network. Overall, Ricacryl®3801 is an unique building block for formulations where hydrophobicity, high photo speed, and high crosslink density are desirable. The less functionalized CN300 series produced films more or less resembling the elastomeric polybutadiene backbone: low tensile and modulus and high elongation. The photo-induced crosslinking only brought the glass transition temperature (Tg) from polybutadiene's intrinsic value of -75°C up to around -40°C. This low temperature transition is critical for delivery of film flexibility desired by electronics and specialty coating applications.


406 3. Ricacryl®3801: Influence of Photoinitiators and UV Dosage on Photo Reactivity and Film Properties As indicated in Table 1, Ricacryl®3801 contains 44 potentially photochemically reactive double bonds among which are: 2 aerylates, 6 methacrylates, 26 1,2 vinyls, and 10 1,4 trans. FTIR was utilized to monitor degree of conversion of different double bonds. Peaks at three distinct wavenumbers, 812 cm" , 910cm" , and 968cm* were used for (meth)acrylic, 1,2 vinyl, and 1,4 trans double bonds, respectively. As one can see from Figure 1, over eighty percent of the (meth)acrylic double bounds were converted during photopolymerization while only twenty seven percent of 1, 4 trans and fourteen percent of 1,2 vinyl double bonds participated in the free radical chain polymerization. Although the 1,4 and 1,2


1

1

1

Table 3. Photo curing speed and physical properties of cured films of (meth)acrylated polybutadiene oligomers Ricacryl

"3801 Rate of surface cure, F P M * Tensile strength, psi ** Elong. @ break % ** Modulus psi**

50 1,659 6.6 52,846

CN301 CN303 CN302 20

20

10

639

166

235

15.2

36.2

35.2

6,979

724

1,185

28 75 48

Photoinitiated Polymerization - American Chemical Society

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