Hello!

I am looking for an explanation of shape memory polymers.  

I understand that a shape memory polymer may be deformed to a new
shape above the glass transition temperature and upon cooling back
below the same, the polymer retains the deformed shape (i.e. the
deformed shape is 'set'). Now, when the polymer is heated once again
above the glass transition temperature, the polymer gets rid of this
'set' deformed shape and re-assumes its original shape. Am I correct?

If the glass transition temperature is 30 degrees Centigrade and the
polymer is heated to say 35 degrees and deformed by applying force
would that be sufficient to 'set' the new shape? Or should the
temperature be increased to a substantially higher degree (say 100
degrees C or so) to 'set' the deformed shape?

Also, are such shape memory polymers generally flexible below the
glass transition temperature or are they rigid?

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Request for Question Clarification by feilong-ga on 24 Jul 2003 07:55 PDT

Hi Tvr,

There is a company that specializes on this type of material and they
have some good explanations on their website. I'm not an expert on
this subject but I once wrote an article regarding this type of
material and based it on the info that are presented on their website.
I can try and answer your question based on their given info and give
you the website so that if you have further questions, you can contact
them for more details. Would you be willing to accept this as an
answer?

Regards,
Feilong

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Clarification of Question by tvr-ga on 24 Jul 2003 13:08 PDT

Hello Feilong:

Thank you. I do have a basic understanding of shape memory materials
and have gone through a few websites such as:

http://www.sma-inc.com/
http://www.sma-inc.com/smapaper.html
http://www.sma-mems.com/

but these deal with shape memory alloys (and not polymers). For, shape
memory polymers I have taken a look at http://www.mnemoscience.de/ and
similar sites.

I'm looking more for clarification to my doubts than for general
information. I'll be happy to give a $4 tip for providing specific
answers with relevant links.

Thanks.

Shape memory polymers consist of two immisible polymer networks.  The
higher melting polymer A determines the stress-free relaxed shape. 
This shape is determined by heating the mixture above Tma.  The
second, lower melting polymer B is what affects the stress applied to
the first polymer A.  When the mixture is heated above the melting
temp Tmb of the polymer B and strain is applied to the semi-plastic
object while it cools back below the Tmb, then the strain is
temporarily locked in.  Upon heating above the Tmb again in an
unstressed situation, the object reverts to its original shape.  See
Angew. Chem. I.E 41, 2034 (2002) for more complete explanation.

hi
can you point me out to a comprehensive link on shape memory polymers
on the net.?if we need 2 polymers to have shape memory effect,how is
that new products and developed onyl with one polymer such as
polyurethane or polynororborene etc .