Polycarbonate-Polysiloxane-Based Interpenetrating Networks

Chapter 25

Polycarbonate-Polysiloxane-Based Interpenetrating Networks 1

1

1

Sylvie Boileau , Laurent Bouteiller , Riadh Ben Khalifa , Y i Liang1, and Dominique Teyssié

Downloaded by UNIV OF PITTSBURGH on December 18, 2014 | http://pubs.acs.org Publication Date: May 4, 2000 | doi: 10.1021/bk-2000-0729.ch025

2

2

1Laboratoire de Recherche sur les Polymères, U M R 7581-CNRS, B.P. 28, 2 rue Henri Dunant, 94320 Thiais, France Université de Cergy-Pontoise, Neuville sur Oise, Département de Chimie, 5 mail Gay-Lussac, 95031 Cergy-Pontoise Cedex, France

Interpenetrating polymer networks based on polysiloxanes (PS) and polycarbonates (PC) were prepared by the in-situ method : a polysiloxane bearing various proportions of RT crosslinkable -Si(OEt)3 side groups and hydrolyzable phenylcarbonate moieties was mixed with diethyleneglycol bis-allylcarbonate and benzoyl peroxide. After the formation of the PS network at R T , the crosslinking of the PC network was achieved at 100°C. Various chemical modifications of the PS component in the IPN were performed in order to improve the degree of interpenetration as checked by turbidity, D S C and D M A measurements. Kinetics of phenol release was studied on linear PS, single PS networks, semi-IPNs and IPNs of various compositions in buffered medium (pH = 7.5) at 37.5°C. First-order phenol release rate constants decrease on increasing the crosslinking densities of the systems.

Interpenetrating polymer networks (IPNs) are combinations of crosslinked polymers held together by permanent entanglements (1,2). Due to their interlocking configuration, the state of phase separation obtained at the end of their synthesis is frozen so that their properties are not influenced by ageing and they are well suited for combination of highly incompatible polymer pairs. A number of IPNs based drug delivery systems have been described where the drug is physically embedded in a gradient type IPN (2). We wanted to design a system where the drug delivery would be under chemical control, i.e. a pH-mediated hydrolysis rather than only diffusion controlled in order to prepare a therapeutic lens model. The choice of the two polymeric partners was thus made according to the specific requirements for this application : the optical and mechanical properties where brought by a polycarbonate component, the flexibility and oxygen permeability came from a drug modified polysiloxane component. The drug was covalently bound onto the polysiloxane partner through a spacer containing a carbonate linkage. This function conveniently hydrolyzes at pH 7.5 which corresponds to the pH value in the tear medium.

© 2000 American Chemical Society In Silicones and Silicone-Modified Materials; Clarson, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2000.

383


384

Moreover the presence of a carbonate group close to the siloxane backbone was expected to help the compatibilization with the polycarbonate component. Simultaneous and sequential IPNs based on various polymeric systems have been prepared using polydimethylsiloxane (PDMS) as the host network (3-8). These systems include poly(ether-urethane), polystyrene, poly(2,6-dimethyl-1,4phenyleneoxide), polyacrylic acid, PDMS, polymethylmethacrylate, polyethylene oxide (PEO) ... as the guest network. Some semi-interpenetrating networks (s-IPNs) based either on a linear polymer embedded in a polysiloxane network (5,9,10) or on a linear polysiloxane combined with a PEO network (8) have also been described. In some cases, PDMS has been replaced by polyaromatic siloxanes such as polydiphenyl or polymethylphenylsiloxanes (10-12). The focus of this paper concerns the preparation and properties of IPNs and s-IPNs based on polysiloxanes and poly(diethyleneglycol bis-allylcarbonate) (13,14). Experimental Polymethylhydrogenosiloxane (PMHS),

DP

n

= 35 (Merck), allyltriethoxysilane

(ATES), (ABCR), benzoylperoxide (BPO), (Fluka), dibutyltin dilaurate (DBTDL), (Merck), platinum methylvinylcyclosiloxane complex (PCO 85), (ABCR), were used as received. Diethyleneglycol bis-allylcarbonate (XR 80), (Essilor) was purified on a silica gel column. Butenylphenylcarbonate (BPC) was prepared by reaction of phenyl chloroformate with 3-buten-l-ol under phase transfer catalysis conditions (13,15). Precursors PSIa, PSIb and PSIc (Scheme 1) were prepared by cohydrosilylation with PMHS of both A T E S and B P C in various relative proportions. The hydrosilylation reactions were carried out in dry toluene at 6 0 ° C with a Pt° complex catalyst ([-CH=CH ]/[SiH] = 1.1 ; [Pt]/[SiH] = 5.10-4). 2

O C

H

a

~?*'

H

C H -1$i - ( C H ) - O - C - O -O 3

2

^

± n CH -Si-(CH ) -Si(OEt)3

Q

3

+ n CH =C H - ( C H ) - 0 - C - O ^ Q 2

2

2

+ m C H = CH-CH -Si(OEt) 2

4

2

2

3

^ ^ ' ' ^ = 5 %

3

PSIb: n=75% m=19% PSIc : n=55% m=40% Single drug-polysiloxane network crosslinking : 2% D B T D L , 20°C Scheme 1, The reaction was followed by monitoring the decrease of the SiH IR band at 2160cm' . The polymers were recovered by precipitation in methanol, purified with carbon black treatment in diethylether, precipitated again in methanol and dried under high vacuum (yields « 80%). As checked by *H NMR, the final proportions of ATES 1

In Silicones and Silicone-Modified Materials; Clarson, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2000.


385

and BPC grafted onto the polysiloxane main-chain were 0% and 95%, 5% and 85%, 19% and 75%, and 40% and 55% for PSO, PSIa, PSIb and PSIc respectively. The remaining 5% side-functions on each polymer are either unmodified SiH groups (residual signal at 4.7 ppm on the *H N M R spectrum, see Figure 1), or phenoxy groups (6.95 ppm) resulting from a side-reaction (15). Single polysiloxane networks PSIaN, PSIbN and PSIcN were obtained by adding D B T D L (2% by weight) which catalyzes the crosslinking at room temperature which occurs through the Si(OEt)3 groups. The polycarbonate network was prepared by freeradical polymerization of X R 80 with BPO as the initiator (3% by weight) at 95°C for 1 h, under nitrogen. The amount of extracted products measured after Soxhlet extraction with CH2CI2 was lower than 5% and the amount of unreacted double bonds as measured by iodometry was equal to 11%. A series of s-IPNs was prepared from various weight proportions (20%, 35%, 50%, 65%) of PSO embedded in a PC network which was cured with BPO (3% by weight) at 95°C for 8h. Finally the IPNs were synthesized by a two step in-situ method. The carbonate monomer, BPO, the modified polysiloxane (PSIa, PSIb or PSIc) and D B T D L were mixed together under nitrogen. The mixture was allowed to react at room temperature until the polysiloxane was crosslinked (15 to 20h) and the temperature was then raised up to 100°C in order to promote the PC network formation (Scheme 2). Bis allyl carbonate / BPO

20°C, 20h

Polysiloxane network

polycondensation

swollen by carbonate monomer

Drug modified polysiloxane / D B T D L 0.1/0.9 to 0.9/0.1 weight proportions

free-radical polymerization

Scheme 2.

100°C, 6h BPO 3%

IPN

1 3

*H and C N M R spectra were recorded in C D C I 3 at 2 0 ° C on a Bruker A M 200SY apparatus. The Tg values were taken as the onset point from the second heating curves recorded at a 20°C/min heating rate. D M A measurements were performed on a Perkin-Elmer D M A 7 apparatus with a 10°C/min heating rate and at a frequency of 1 Hz. The kinetics of the phenol release were studied on ca. 1 g samples immersed in 100 ml pH=7.5 phosphate buffer at 37.5 °C. 1 ml aliquots of the buffer solution were then extracted with diethylether and the phenol concentration was determined by U V 1

1

spectroscopy on a Perkin-Elmer 544 spectrometer at 273 nm (8=22001 mol" cm" ). Results and Discussion A series of IPNs was prepared from PSIa, PSIb and PSIc on one hand and polycarbonate PC on the other hand. The relative weight proportions of the two networks were varied between 10 and 90% and the resulting IPNs showed less than 8% extracted material in all cases. The IPNs prepared from the PSIb and PSIc series were all transparent which is indicative of a satisfactory level of interpenetration considering the fact that the refractive indices of the two partners are different.



X

6

\

X''y

O

O

:

6.5

10.11 12

A Xk

3

CH ™Si-O I O

3

2 2

3 2

7.5

4

5 2

-

6

6.0

10

7.0

12

'

C 4 . 0 5 . S PPH )

PS > 4.2 7.7 5.0 8.0 5.6 C 10 (mol/l) ) b

a

4

c

0

3

80

1

k 10 (day- ) a

b

42

24

25

«6

) PMHS modified with 80% PEO 350 grafts and 20% BPC units (18) ) [Si(OEt)3]=19 mol%; ) initial phenol concentration in the medium. c

The very large differences in the rates of the phenol release in each of the studied systems suggested that a chosen kinetics of release could probably be obtained by adjusting the parameters which control the rate of hydrolysis of the carbonate bond in the IPN and the release of the phenol out of the system. The accessibility of the carbonate function to the hydrolyzing agent and the diffusion of phenol out of the system will both be controlled by (i) the crosslinking density in each network and (ii) the weight proportions of the two networks in the IPN. Thus a very simple kinetic model was used starting from the following equation (1) expressing the rate constant k


In Silicones and Silicone-Modified Materials; Clarson, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2000. 0

Time(day)

2 0

30

Figure 3. Kinetics of the phenol release in pH=7.5 buffered medium at 37.5°C from different polymeric systems, • PSO; • 1:1 PSO/PC sIPN; O 1:4 PSO/PC sIPN; • 1:1 PSIb/PC IPN.

10


40

391

of the delivery (each term in this equation being determined experimentally on independently synthesized systems as will be described below): k=k -ki8ial-k 8 0

-81 and 8

2

2

2

(1)

a 2

are the respective crosslinking densities in the polysiloxane and the

polycarbonate networks. 81 values were calculated from the average molecular weight of the monomer unit and the percentage of crosslinking side-chains in the PSI partners. 8 values were calculated similarly for the PC networks from the measured density, the molecular weight of the monomer and the percentage of the allyl double bond conversion. -ai and a are coefficients for the polysiloxane and polycarbonate networks respectively. -The rate constant ko of the phenol delivery was determined on a system where the crosslinking density is equal to zero, i.e. the 100% BPC modified polysiloxane PSO. It was found to be equal to 4.2 10 d a y . -The ki and k rate constants were determined by studying the kinetics on systems where either of them could be eliminated in turn. Thus k was determined from the rate constants calculated from the kinetics of the phenol release from a series of


2

2

-2

1

2

2

s-IPNs made from uncrosslinkable PSO (8i=0) and PC in 1:4, 1:2, 1:1 and 2:1 weight proportions (Figure 4). The plot of those rate constants versus 8 being linear, a was found to be equal to 1 and the reduced equation in these systems is : 2

k(day ) = 4.2 10" -5.4 8 1

2

2

(2)

2

-Similarly ki was determined on systems where 8 =0, i.e. on single polysiloxane networks formed from PSIa, PSIb and PSIc precursors. The corresponding kinetic plots : L n ([C]/[Co]) versus time are shown in Figure 5. In this case ai=0.6 and the reduced equation is : 2

1

2

0

k(day- ) = 4.2 10" - 5 i -

6

(3)

In each series PSO represents the limit system : it is the limit of the s-IPNs series with a zero proportion of PC and it is also the limit of the single polysiloxane network series with a zero crosslinking density. Combining (2) and (3) relationships and taking x as the weight fraction of carbonate monomer in the IPN and y as the molar fraction of A T E S crosslinkable groups in the PSI partner, the final model equation is : 2

2

2

0

k(day-i) = 4.2 1 0 - 8.2 10" x - 4.5 10~ y -

6

(4)

The validity of this simple model which was derived from measurements on PSO/PC s-IPNs on one hand and on single PSI networks on the other hand was checked on the full IPNs by comparing calculated values to experimentally determined ones. The best fit was obtained between 5 and 40% phenol release showing that truly tailor-made delivery systems can be designed for the specific application.


In Silicones and Silicone-Modified Materials; Clarson, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2000. Figure 4. Kinetics of the phenol release in pH=7.5 buffered medium at 3 7 . 5 ° C from sIPNs, • PSO; V 2:1 PSO/PC; O 1:1 PSO/PC; • 1:2 PSO/PC; A 1:4 PSO/PC sIPNs


In Silicones and Silicone-Modified Materials; Clarson, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2000. Figure 5. Kinetics of the phenol release in pH=7.5 buffered medium at 3 7 . 5 ° C from single networks obtained from different polysiloxane precursors, • PSO; • PSIaN; O PSIbN; • PSIcN.


394

References 1. 2.

3.


4.

5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

Sperling, L . H . Interpenetrating Polymer Networks and Related Materials, Plenum Press, New York, 1981. Sperling, L . H . in Interpenetrating Polymer Networks, Klempner D.; Sperling L . H.; Utracki, L . A . Eds.; Adv. Chem. Ser., A C S Washington D C 1994, Vol. 239; pp. 3-38 Frisch, H.L.; Huang, M . W . in Siloxane Polymers; Clarson, S.J.; Semlyen, J.A. Eds., PTR Prentice Hall, Englewood Cliffs, New Jersey, 1993, pp. 649-667. He, X . W . ; Widmaier, J . M . ; Herz, J . E . ; Meyer, G . C . in Advances in Interpenetrating Polymer Networks; Klempner, D . ; Frisch, K . C . Eds., Technomic Publishing Co., Lancaster, Pennsylvania, 1994, pp. 321-356. He, X.W.; Widmaier, J.M.; Herz, J.E.; Meyer, G.C. Polymer, 1992, 33, 866. Hamurcu, E.E.; Baysal, B . M . Macromol. Chem. Phys., 1995, 196, 1261. Miyata, T.; Higuchi, J-L; Okuno, H.; Uragami, T. J. Appl. Polym. Sci., 1996, 61, 1315. Grosz, M . ; Boileau, S.; Guégan, P.; Cheradame, H.; Deshayes, A. Polym. Prep., 1997, 38(1), 612. Frisch, H.L.; Chen, X . J. Polym. Sci., Polym. Chem., 1993, 31, 3307. Gilmer, T . C . ; Hall, P.K.; Ehrenfeld, H . ; Wilson, K . ; Bivens, T.; Clay, D.; Encheszl, C. J. Polym. Sci., Polym. Chem., 1996, 34, 1025. Klein, P.G.; Ebdon, J.R.; Hourston, D.J. Polymer, 1988, 29, 1079. Caille, J.R. Thèse de Doctorat, Univ. P. et M . Curie, Paris 6, 1997. Ben Khalifa, R. Thèse de Doctorat, Univ. P. et M . Curie, Paris 6,1994. Boileau, S. ; Bouteiller, L . ; Ben Khalifa, R. ; Liang, Y . ; Teyssié, D. Polym. Prep., 1998, 39 (1), 457. Yu, J.M.; Teyssié, D.; Boileau, S. Polym. Bull., 1992, 28, 435. Frisch, K . C . ; Klempner, D. ; Midgal, S. ; Frisch, H.L. ; Ghiradella, H . Polym. Eng. Sci., 1974, 14, 76. Blundell, D . J . ; Longman, G.W. ; Wignall, G.D. ; Bowden, M.J. Polymer, 1974, 15, 33. Yu, J.M. Thèse de Doctorat, Univ. P. et M . Curie, Paris 6, 1992.


Polycarbonate-Polysiloxane-Based Interpenetrating Networks

Recommend Documents