RADIATION PREPARATION OF SOME INTERPENETRATING POLYMER NETWORKS INCLUDING NATURAL POLYMER AS THE SECOND COMPONENT

It is well known that the mutil-component polymers, such as the interpenetrating polymer networks (IPNs) which have the microphase-separated structure, exhibit good blood compatibility when they are used in biomedicine, biotechnology and DDS. Here the authors are interested in developing the IPN hydrogels in which the temperature sensitivity of the main component, polyNIPAAm could be effectively kept by changing the content of second components in the IPNs. Two kinds of IPNs were prepared by J-irradiation technology and some of their properties were investigated.

3.1. Semi-IPNs hydrogels composed of PNIPAAm and hydrophilic polymers 3.1.1. Radiation preparation

In this work, T, C and S were defined by

T = (Wm + Wc + Wp)/Vsu 100%, C = Wc/Wmu100%, S = Wp/Wmu100%

where Wm, Wc and Wpare weight of monomer (NIPAAm), crosslinking agent(Bis) and polymer, respectively. Vs is the whole volume of the solution (mL). Semi-IPNs hydrogels have been prepared by radiation of aqueous solutions of PNIPAAm and different hydrophilic polymers at room temperature.

3.1.2. The effect of linear hydrophilic polymer components on the swelling behaviour of semi-IPNs

From Fig. 4 it can be seen that the incorporation of polyNaAAc in semi-IPN hydrogels had much higher swelling ratio than pure PNIPAAm. On the other hand, the higher the molecular weight of polyNaAAc used, the greater the swelling ratio of the semi-IPNs.

According to hydrophilicity of the second components in the semi-IPNs, the swelling capacity of polyNIPAAm/polyNaAAc IPNs was higher than that of polyNIPAAm/PVP IPNs and polyNIPAAm/PVP IPNs, respectively (see Fig. 5)

3.1.3. Temperature sensitivity and pH effect of polyNIPAAm/polyNaAAc

The semi-IPNs of polyNIPAAm/polyNaAAc hydrogels still kept obvious temperature sensitivity but the two others did not and the swelling ratio was increasing with pH value in the swelling solutions (see Fig. 6 and Fig. 7).

FIG. 4. The effect of polyNaAAc on the swelling behaviour of semi-IPNs at room temperature. A:

polyNIPAAm, B: polyNIPAAm/polyNaAAc(Mw = 16000–18000) C: polyNIPAAm/polyNaAAc (Mw

= 7000–8000), 3kGy, 103 Gy/min.

FIG. 5. Comparative swelling behaviour curves of semi-IPNs polyNIPAAm/x hydrogels at room temperature. X = polyNaAAc(A), PVA(B), PVP(C) 5kGly, 103 Gy/min.

FIG. 6. Comparative EDS-T curves of semi-IPNs polyNIPAAm/x hydrogel, x = polyNaAAc(A), PVA(B), PVP(C), 5kGy, 103 Gy/min.

FIG. 7. pH effect on the swelling behaviour of semi-IPNs polyNIPAAm/polyNaAAc at room temperature.

3.1.4. The Swelling-shrinking cycles

All the semi-IPNs of polyNIPAAm/PAAc with different content of second polymers still kept obviously thermally reversible property after several swelling-shrinking cycles but the time for swelling to equilibrium was larger than that for shrinking (see Fig. 8)

3.2. The IPNs composed of polyNIPAAm and PMMA 3.2.1. Radiation preparation

The IPNs were prepared by the sequential method. 16.8kGy of dose was used to form matrix polymer polyNIPAAm. The second step was to swell the pieces of polyNIPAAm dry gel in DMSO solution of MMA. The swollen polyNIPAAm were irradiated again with 8.4kGy. Purification and drying treatment.

3.2.2. Swelling behaviour

From Fig.9 it can be seen that with increasing content of PMMA in the IPNs, the swelling ratio of the IPN gels decreased obviously and the time to equilibrium of swelling was shorten as well.

3.2.3. The temperature sensitivity of the IPNs

The IPN hydrogels with PMMA still kept the temperature sensitivity but the LCST was lower than that of pure PNIPAAm due to the hydrophobicity of PMMA (sees Fig. 10).

Swelling-shrinking cycle tests of NIPAAm/MMA IPNs showed that these hydrogels were quite stable after several cycles (see Fig. 11)

3.2.4. MB release from the IPNs

The MB release from PNIPAAm hydrogels into water was faster than that from IPN hydrogels that can be explained by structure of IPNs gels with MMA (Fig. 12)

3.3. Radiation synthesis and characteristic of KC/PVP blend hydrogels

Kappa-Carrageenan (KC) is a kind of natural polymer, polysaccharide, white or light brown pellet/powder. KC can be dissolved in 80^oC hot water and formed the transparent and viscous liquid. After cooling to room temperature, KC liquid became KC hydrogel (a kind of thermal reversible gel) which is quite stable and behaves with certain mechanical strength. KC is mainly used in food and drug industry.

In this work a series of blend hydrogels were prepared from KC and PVP by J-irradiation and some of the improved properties which can be used in biomedical and biotechnology were measured. The discussion of mechanism was given.

3.3.1. Radiation degradation of KC gels

Like the common natural polymer, KC is also a kind of radiation degradation polymer.

(see Fig. 13)

3.3.2. Blend hydrogels composed of KC and PVP 3.3.2.1. Preparation of KC/PVP blend hydrogels

Various contents of KC or KC/PVP aqueous solutions were prepared by dissolving KC or KC/PVP in distilled water at 80^oC for 2h. Then the hot mixture was poured into glass tube of 15 mm in diameter. The cooled samples became hydrogels and were irradiated by ⁶⁰Co J rays at room temperature.

3.3.2.2. The property tests of the blend hydrogels

The gel strength and swelling ratio of the KC/PVP blend hydrogels appeared unexpected increase simultaneously with the increasing of KC content within a certain dose (see Fig. 14 and Fig. 15).

Besides KC blending with PVP, the radiation preparation of KC/PVP hydrogels by KC mixing with N-VP/14G also be studied. The results indicated that the change of the gel strength and swelling ratio is almost the same as those of hydrogels prepared by KC blending with PVP.

An excellent blend hydrogels can be obtained by adjusting each condition and it would be very useful in biotechnology.

3.3.2.3. Discussion on mechanism Before irradiation

In KC/PVP gel the small molecules of N-VP or linear PVP chains were dispersed homogeneously in the network of physical crosslinked KC due to their hydrophilicity

Low doses

During low doses (10~40kGy), the radiation polymerization of N-VP and radiation crolsslinking of PVP (especially in the presence of crosslinkers) would be performed prior to radiation degradation of KC molecules, which means that the molecular chains and physical crosslinking points of KC would be protected by the radiation effect of N-VP and PVP. As polymerization and crosslinking of N-VP and PVP are going on, the IPNs were formed practically.

High doses

When the polymerization of N-VP and crosslinking of PVP have finished, the extra radiation energy would make KC degrade and the structure of KC/PVP IPNs were destroyed which resulted in decrease of gel strength and swelling ratio.

4. PRE-IRRADIATION GRAFTING CO-POLYMERIZATION OF NIPAAM AND