Phase Mixing in Urethane Polymers - American Chemical Society

23 Phase Mixing in Urethane Polymers

Downloaded by UNIV OF MASSACHUSETTS AMHERST on March 7, 2016 | http://pubs.acs.org Publication Date: November 30, 1981 | doi: 10.1021/bk-1981-0172.ch023

ROBERT J. LOCKWOOD and LOUIS M. ALBERINO Donald S. Gilmore Research Laboratories, The Upjohn Company, North Haven, CT 06473

It has become well established (1-8) that urethane polymers are two-phase segmented block copolymers. The blocks consist of hard segments formed from the isocyanate and the short chain diol and soft segments formed from the isocyanate and long chain polyol. The interconnection between these two phases and the degree of phase separation are of major importance in determin ing the final polymer properties. (9-14,16,17) If a polymer system consisted of compatible segments which were not phase separated then properties such as glass transition are considerably different from the case where the segments are incompatible and, hence, phase separated. In this research, the concept of compatible and incompatible hard and soft segments was investigated by first looking at physical mixtures of model amorphous hard segments and model soft segments. The physical blends then were analyzed by DSC and the glass transitions were measured. DSC has been demon strated, to be a very useful tool for studying polymer morphol ogy. (15) If the mixture of the amorphous hard and soft segments was compatible then one glass transition should result. However, if the mixture was incompatible, then the individual distinct Tg's would be observed. These ideas were further extended to actual polymers which were produced from prepolymers and various extender/polyol combinations. Experimental The extenders used were urethane grade dipropylene glycol (DPG) obtained from Dew Chemical, and urethane grade 1,4 butanediol (1,4-BDO) obtained from GAF Corporation. The polyols used were Poly G 53-56 (Olin Chemical) a 2000 molecular weight polyoxyethylene-oxypropylene diol containing 11% BO (ethylene oxide), Poly G 55-56 (Olin Chemical) a 2000 M.W. polyoxyethylene-oxypropylene diol containing 45% BO, and Niax PPG-2025 0097-6156/81/0172-03 63$05.00/0 © 1981 American Chemical Society

Edwards et al.; Urethane Chemistry and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

364

URETHANE CHEMISTRY AND APPLICATIONS

(Union Carbide) a 2000 M.W. polyoxypropylene glycol containing no EO. The isocyanate used was Upjohn 125M, 4,4' diisocyanato diphenyl methane (MDI). Polyols and extenders were dried by degassing under vacuum.


Model Preparation In order to provide s o l u b i l i t y , the MDI-DPG model oligomeric hard segment was prepared at a hydroxyl to isocyanate equivalent ratio of 1.0 to 0.9. The model soft segments were prepared at 1 to 1 equivalent ratios. Both hard and soft segments were pre pared by mixing the two components together at 50°C with (0.01%) dibutyl t i n dilaurate catalyst i n p l a s t i c cups. The model hard and soft segment mixtures were then dissolved i n reagent grade Ν,Ν-dimethyl formamide (stored over sieves - Fisher) and cast into glass c r y s t a l l i z i n g dish covers. The solvent was gemoved by oven drying at 80 C followed by vacuum drying at 110 C for two hours. TGA shewed the resulting material to be solvent free. DSC scans on these materials were then run on a DuPont 990 at 10 C/min. under nitrogen from -100°C to +250 C. Polymer Preparation Preparation of the polymers was carried out by a two step method. F i r s t , MDI prepolymers were prepared i n a 5 l i t e r round bottom flask equipped with a s t i r r e r , thermometer, addition funnel, and nitrogen i n l e t . The dried polyols were added dropwise to MDI at 75 C and the reaction temperature was maintained at 85 C. The mole ratios of MDI to polyol l i s t e d i n Table I I gave prepolymers containing 18.67% free NCO groups by weight or an isocyanate equivalent weight of 225. In the case of prepolymers 2 and 4, the DPG was added f i r s t and then the 2000 molecular weight polyol was added. In the second step, the urethane polymers were prepared from each of the four prepolymers by mixing with a stoichiometric amount of 1,4-butanediol (1,4-BDO). To a p l a s t i c cup was added 125 grams of prepolymer, 25 grams of 1,4-BDO, and 0.1 cc of UL-1, a dibutyl t i n mercaptide from Witco Chemical Co. These rocm temperature components were mixed for 10 seconds using a high shear ndxing blade at 2400 rpm. The prepared polymers were allowed to cure at rocm temperature for at least one week and then DSC*s and ΊΜΑ s were run. DSC s were run on a DuPont 990 at 10 C/min. with a nitrogen purge. One sample series was run over the range -120 C to 0 C and another sample series was run from 20°C to 250°C. TMA.'s were run over a temperature range of -20 C to 210 C on a Perkin Elmer Thermcariechanical Analyzer TMS-1. They were run with a 40 mil diameter penetration probe loaded with 200 grams to give a pressure of 394 p s i . The program rate was 10 C/min. under a helium atmosphere and the Y-axis sensitivity was 10 inches/inch of chart paper. 1

1

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LOCKWOOD AND ALBERiNO

23.

Phase Mixing in Urethane Polymers 365

Results and Discussion MDdel hard segments of MDI-DPG at a 0.9/1.0 mole ratio gave a Tg of 85 C which was used i n the physical blending study, while at a 1.0/1.0 mole ratio gave a Tg of 110°C. No melting endotherms were observed so these hard segments are described as glassy-amorphous. . Model soft segments of MDI/PPG-2025, MDI/Poly 053-56, and MDI/Poly G-55-56 gave Tg's of -50°C, -52°C, and -56 C, respectively (see Table I ) . As such, these amorphous (glassy) hard segments and amorphous (rubbery) soft segments folloWgClassical rules of mixing. For example, the Fox e q u a t i o n — ^ f o r the Tg of a compatible blend i s given by (1),


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= glass transition of Polymer A (°K) = weight fraction of Polymer A.

Thus, i f two polymers are compatible - SINGLE PHASE - there w i l l be one Tg given by equation (1). I f two polymers are i n compatible - Tm PHASES - there w i l l be two Tg's - those of the individual polymers. These concepts are demonstrated i n Figure 1 which shows blends of the hard segment (MDI-DPG) i n soft segments (MDI/Poly G 53-56™ and MDI/Poly G 55-56 ). Figure 1 shows that the hard segment MDI-DPG i s e s s e n t i a l l y completely compatible i n the soft segment MDI/Poly G-55-56, a 45% B0 polyol and essentially completely incompatible i n the soft segment MDI/Poly G-53-56, an 11% E0 polyol. The theoret i c a l line derived fran Equation 1 i s i n good agreement with the compatible blend. An example of a crystalline hard segment i s MDI/1,4-BD0 which has a Tm or melt point by DSC. Table 1 shews that MDI/1,4BD0 hag a small Tg at 110°C, a Tc or c r y s t a l l i z a t i o n temperature at 182 C and a series of three successive c r y s t a l l i t e melting points at 202°C, 220°C, and 236 C; the upper temperature being the mp of the pure equilibrium c r y s t a l . The same c c m p a t i b i l i t y / i n c x ^ a t i b i l i t y rules as discussed for amorphous hard segments and soft segments do not apply with crystalline hard segments. Extenders which form crystalline hard segments with MDI aggregate into bundles or form a hard segment domain within the amorphous soft segment phase (3). Thus, crystalline hard segment based polymer systems w i l l generally have separate hard and soft segment glass transitions.



Mole R a t i o 1/1 1/1 1/1

MDI - PPG-2Q25® MDI - P o l y G-53-56® MDI - P o l y G-55-56®

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-50 -52 -56

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DSC ANALYSIS OF HARD & SOFT URETHANE SEGMENTS

TABLE I

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Phase Mixing in Urethane Polymers 367

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1.0 0.5 0 Fraction, Soft Segment Wt. Figure 1. DSC results of physical blending of hard and soft segments. Key: ψ , MDI-DPG/M DI-Poly G (55-56 ®); O, 0 , and Δ, MDI-DPG/MDl-Poly G (53-56 ®).


368



Table I I l i s t s t h e thermal t r a n s i t i o n s by DSC and ΊΜΑ o f f o u r d i f f e r e n t urethane polymer systems based on t h e p r e c e d i n g hard and s o f t segment combinations. While PPG-2025 was used i n p l a c e o f P o l y G-53-56, i t should behave t h e same s i n c e i t has no c c m p a t i b i l i z i n g BO. F i g u r e s 2 and 4 e x h i b i t t h e r e s p e c t i v e DSC and ΊΜΑ c u r v e s o f these polymers: tm

Polymer 1 based on MDI/PPG-2025 /l, 4-BDO shows an i n compatible two phase polymer w i t h a w e l l d e f i n e d s o f t segment Tg a t -40 C and sharp m e l t i n g endotherms a t 203 C, 222 C, and 238 C c h a r a c t e r i s t i c o f a pure MDI/1,4-BDO hard segment. The IMA. c u r v e has an i n i t i a l s o f t e n i n g at 41°C, a second s o f t e n i n g a t 130 C and a major s o f t e n i n g a t 165 C. T h i s two s t e p s o f t e n i n g might be due t o t h e i n f l u e n c e o f the w e l l d e f i n e d s o f t seg ment domains i n t h e hard segment domain. Q

tm

Polymer 2 based on MDI/DPG/PPG-2025 /l, 4-BDO i s a l s o two phase; however, t h e c r y s t a l l i n e hard segment phase has been transformed t o a glassy-amorphous phase as shown by the Tg a t 105°C and the s o f t segment g l a s s t r a n s i t i o n i s n o t as w e l l - d e f i n e d as i n Polymer 1. The major s o f t e n i n g observed a t 99 C by ΤΜΆ v e r y c l o s e l y corresponds t o t h e 105°C Tg measured by DSC. 0

Polymer 3 based on MDI/Poly G SS-sd ^/!, 4-BDO e x h i b i t s an i n c o m p a t i b l e two phase polymer c o n s i s t i n g o f an amorphous s o f t segment Ttj a t -38 C and c r y s t a l l i n e hard segment Tin's a t 222 C and 241 C. ΊΜΆ shews a high 160°C o n s e t s o f t e n i n g temperature and a major s o f t e n i n g a t 205 C, which i s v e r y c l o s e t o the m e l t temperature o f t h e hard segment. Q

o

Polymer 4 based on MDI/DPG/Poly 0-55-56^/1,4-BDO can be d e s c r i b e d as a b a s i c a l l y one-phase compatible polymer system. The s o f t segment Tg i s almost n o n - e x i s t e n t and t h e r e i s no d e f i n a b l e Tm. Extreme i n t e r m i x i n g between t h e h a r d and s o f t segments has taken p l a c e , r e s u l t i n g i n an i n t e r m e d i a t e g l a s s y amorphous Tg by DSC o^ about 81 C. The ΊΜΑ c u r v e shews a major s o f t e n i n g a t about 74 C, which once a g a i n i s i n c l o s e agreement w i t h t h e Tg by DSC. Conclusions P h y s i c a l b l e n d i n g o f model hanopolymers can be used t o p r e d i c t t h e c o m p a t i b i l i t i e s o f urethane hard and s o f t segments and agrees w e l l w i t h a c t u a l r e a c t i o n b l e n d i n g . As shown fcy p h y s i c a l b l e n d i n g s t u d i e s MDI-DPG i s compatible w i t h a 2000 M.W.-45% BO c o n t a i n i n g polypropylene g l y c o l based p o l y o l , and i n c o m p a t i b l e w i t h a 2000 M.W. - 11% EO c o n t a i n i n g p o l y p r o p y l e n e g l y c o l based p o l y o l . When urethane polymers based on the above o r s i m i l a r p o l y o l s had 25% o f the hard segment based on MDI-DPG


LOCKWOOD AND ALBERINO

Phase Mixing in Urethane Polymers

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Phase Mixing in Urethane Polymers

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372


and 75% of the hard segment based on MDI/1,4-BD0, the compatibi l i z i n g influence o f the MDI-DPG predominated. This level of MDI-DPG was found to destroy the c r y s t a l l i n i t y of a normally c r y s t a l l i n e 1,4-butanediol hard segment, making the t o t a l hard segment glassy-amorphous and produced a basically one-phase compatible polymer when a high BO (45%) containing polyol i s used. Thus, the level of MDI-DPG i n a urethane polymer can be c r i t i c a l to the polymer's performance and f i n a l properties. Urethane polymer morphology can be quickly characterized by means of DSC and ΊΜΆ analyses. These thermal analyses are valuable tools i n determining the interrelationship of the many formulation variables of urethane polymer systems: polyol type and molecular weight, hard segment type and concentration, and various prepolymer compositions.

Literature Cited 1.

Clough, S. Β., and Schneider, N. S., J. Macromol. Sci., 1968, B2, 553. 2. Clough, S. Β., Schneider, N. S. and King, A. O., J. Macromol. Sci.-Phys., 1968, B2(4), 641. 3. Estes, G. M., Cooper, S. L. and Tobolsky, Α. V., J. Macromol. Sci.-Rev. Macromol. Chem., 1970, C4(2), 313. 4. Samuels, S. L. and Wilkes, G. L., J. Polym. Sci., 1973, 43, 149. 5. Seymour, R. W., Allegrezza, A. E.,Jr., and Cooper, S. L . , Macromolecules, 1973, 6(6), 896. 6. Chang, Y. P., and Wilkes, G. L., J. Polym. Sci., 1975, 13, 455. 7. Blackwell, J . and Gardner, Κ. H., Polymer, 1979, 20, 13. 8. Bonart, R., Morbitzer, L . , and Hentze, G., J . Macromol.Sci., Phys., 1969, 3(2), 337. 9. Harrell, L. L . , J r . , Macromolecules, 1969, 2(6), 607. 10. Huh, D. S., and Cooper, S. L . , Polym. Eng. and Sci., 1971, 11(5), 369.

11. 12. 13. 14. 15. 16. 17. 18.

Ng, Η. Ν., Allegrezza, Α. Ε., Seymour, R. W., and Cooper, S. L . , Polymer, 1973, 14, 255. Smith, T. L . , J . Polym. Sci. - Phys., 1974, 12, 1825. Zdrahala, R. J., Gerkin, R. M., Hager, S. L . , and Critchfield, F. E . , J . Appl. Polym. Sci., 1979, 24, 2041. Seefried, C. G., J r . , Koleske, J . V., Critchfield, F. E., J. Appl. Polym. Sci., 1975, 19, 2493, 2503, 3185. Seymour, R. W., and Cooper, S. L . , Polymer Letters, 1971, 9, 689. Samuels, S. L. and Wilkes, G. L., J . Polym. Sci., 1973, 11, 807. Seymour, R. W., and Cooper, S. L . , Macromolecules, 1973, 6, 48. Fox, T. G., Bull. Amer. Phys. Soc., 1956, 2, 123.

RECEIVED April

30, 1981.


Phase Mixing in Urethane Polymers - American Chemical Society

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