The materials are: Methyl methacrylate (MMA), poly(ethylene glycol)n dimethacrylate (PEGDMA) with molecular weights of Mn=750, and photoinitiator 2,2-dimethoxy-2-phenylacetophenone (DMPA).
If I use only MMA, and PEGDMA and use adequate heating or magnetic stirring with heating, can I synthesize Shape Memory Polymer using these two chemicals?
In reference, Photoinitiator (DMPA 0.2 % --- 0.4 %) and UV exposure (30 minutes) are also mentioned.
I am using the method described in the article but unable to synthesize in proper form. The samples are not really elastic and they break when bend/twist. I attempted the synthesis process in the following way:
Assume that Total Solution = 3 g
PEGDMA MMA DMPA
25% = 0.75 g 75% = 2.25 g 0.4% = 0.012 g
50% = 1.5 g 50% = 1.5 g 0.4% = 0.012 g
75% = 2.25 g 25% = 0.75 g 0.4% = 0.012 g
PEGDMA and MMA constitute 100% solution and a fix amount of DMPA (0.4% of Total solution) is added in each sample. Is it correct way?
I mix all three in these compositions in a beaker and then pour onto a glass substrate covered by Kapton Tape which confines the solution in the surrounded boundary and ease of separate out after heating. 3 times UV exposure for 10 minutes interval (total 30 minutes) and then heating for 90 degree C (for 1 hour). I noticed that samples are dried after exposed to 20 minutes UV light, nevertheless I completed the heating process to ensure complete photopolymerization.
Any suggestions to improve the composition or materials mixing, increase/decrease the UV exposure, or in heating temperature/duration ? Thank you very much!
I'm not familiar with shape memory polymers but I think if you check the mentioned publication (containing the analysis of a number of monomers) might help you. For polar multifunctional systems the double bond conversion will not be 100% for a well cured and still flexible product. You should measure the conversion. Unfortunately especially higher energy can lead to a cross linking of the polymer influencing the flexibility of the polymer (mid chain radicals). I strongly suggest to adapt the illumination time and eventually the light source, initiator. For example a lab curing unit can cure a sample of around 5 g with a view passes (150Wcm-1, 10 m/s). You see the curing time is strongly dependent form the used equipment. Not using a Initiator is not recommended, within your publication a 360 nm light source is used. If you want to cure the sample without initiator you have to use < 300 nm. Than the penetration depth is not sufficient and homogeneous. A modern approach would be using a LED light source and a liquid initiator like TPO-L.
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Dear Michael,
I got some hints from your reply and I will do next preparation in accordance with it.
Thanks a lot.
Seemingly of some interest concerning to this query subject: J. Hu, "Shape Memory Polymers and Textiles", The Textile Institute and Woodhead Publishing Ltd. / CRC Press, 2007; cf. p. 42.
It seems that you are confusing photo and thermal polymerisation. For either photo or thermal polymerisation methods, you need initiator for formation of the free radicals. PEGDMA is a very slow reacting monomer that has been used as a crosslinker. However, PEGDMA continues to crosslink and this could be one reason why the polymer that you have synthesised is hard. Heating the sample at 90 degrees, doesn't complete the photo-polymerisation process, but helps with the thermal polymerisation (photo = light). I suggest that you look at other monomers to co-polymerise with MMA as well as more suitable photoinitiators. I have experience of polymerisation at both R&D and production scales so happy to answer your further questions.
Dear M. Yasin,
Thanks for your reply. Yes, I was considering the both types of polymerization one and the same thing to reach the ultimate goal (getting the free radicals polymerization). I got confusion from the following statement of the reference article, they write, "Polymerization was performed under a 365nm UB lamp (B100AP: Blak-Ray) for 30 minutes. A thermal post-cure was performed at 90 degree C for 1 hour to help ensure complete polymerization."
In an experiment, I tried two different amounts of Photoinitiator (DMPA) and all other parameters including time duration of UV and thermal cure were fixed/constant. Both samples showed significant change in color. Can we conclude any useful information from this?
In other words, what we can expect by increasing the amount of photoinitiator (DMPA)? Any suggestion, please let me know.
The UV Lamp I am using for synthesis is different (brand, intensity), thus I need to investigate the suitability (time required) by myself. I attempted from 5 minutes to 30 minutes by increment of each 5 minutes, but all were seemingly cured, and I could not get any conclusion. Then, I used 3 minutes and 5 minutes for the same composition of two samples. Before thermal-cure I observed the surface of 3 minute cured sample was little wet and 5 minute sample was completely dried. After 90 minutes thermal cure (at 90 Degree C), I observed that 3 minutes UV-cured sample was relatively more elastic and 5 minutes UV-cured sample was rather less flexible. Can anyone explain these trends?
How to make sure by naked-eye that sample has gone through complete (necessary) photopolymerization? How to make sure that 20 minutes heating is enough or 30, or 60 minutes?
Thanks a lot!
yes it is possible throw blending two polymers.
see this article - Shape‐Memory Effect by Specific Biodegradable Polymer Blending for Biomedical, Macromolecular Bioscience, 2014.
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